The invention relates to combine harvesters and particularly to the return conveyance means that serves to catch falling grain from separating apparatus and convey the caught grain forwardly to a grain pan upstream of a cleaning unit.
For many decades, self-propelled combine harvesters have been used by farmers to harvest a wide range of crops including cereals, maize and oil-seed rape. Typically, a combine harvester cuts the crop material, threshes the grain therefrom, separates the grain from the straw, and cleans the grain before storing in an on-board tank. Straw and crop residue is ejected from the rear of the machine.
WO-2012/095239 discloses a combine harvester having a hybrid-type processor which includes a threshing cylinder that rotates on a transverse axis upstream of a pair of axial rotors. The crop stream is fed into the front side of the threshing cylinder and is conveyed tangentially around the underside thereof in a generally rearward direction. Grain and chaff separated at this stage falls onto an underlying grain pan which is driven in an oscillating manner to convey the grain and chaff rearwardly to a rear edge from where the grain and chaff falls under gravity into a cleaning unit.
The remainder of the crop stream from the threshing process is conveyed rearwardly from the threshing cylinder into separating apparatus which comprises a pair of side-by-side rotors which operate in an axial manner wherein the crop stream is conveyed in a spiral path from front to rear.
During the separating process further grain and chaff is removed from the straw and falls under gravity through a grate onto an underlying return pan which conveys the grain and chaff forwardly to a front edge from where it falls under gravity onto the grain pan. The straw by-product from the separating apparatus is ejected from the rear of the combine.
In a pure ‘axial’ type combine, the conventional threshing cylinder is omitted and both threshing and separation is executed by one or more axial rotors.
The cleaning unit of most combines operates according to a well-established process in which grain and chaff cascading down from the grain pan is subjected to an airstream created by a fan. The airstream blows the lighter chaff and dust rearwardly and out of the combine whilst the heavier grain falls onto and through a series of cleaning sieves before being conveyed to the grain tank.
WO-20121095239 discloses the recognition that improved stratification of the layer of grain and material other than grain (MOG) on the grain pan upstream of the cleaning unit improves the cleaning process. Lighter material tends to the top of the layer whilst the grain settles on the bottom. When subjected to the cleaning airstream, the MOG is carried away from the grain layer more effectively.
There is a desire to improve the stratification of the crop material on the grain pan immediately upstream of the cleaning unit.